n a withering assault on the onshore wind turbine industry, the Duke said the farms were “a disgrace”.

He also criticised the industry’s reliance on subsidies from electricity customers, claimed wind farms would “never work” and accused people who support them of believing in a “fairy tale”.

The Duke’s comments will be seized upon by the burgeoning lobby who say wind farms are ruining the countryside and forcing up energy bills.

Criticism of their effect on the environment has mounted, with The Sunday Telegraph disclosing today that turbines are being switched off during strong winds following complaints about their noise.

The Duke’s views are politically charged, as they put him at odds with the Government’s policy significantly to increase the amount of electricity generated by wind turbines.

The country has 3,421 turbines — 2,941 of them onshore — with another 4,500 expected to be built under plans for wind power to play a more important role in providing Britain’s energy.

Chris Huhne, the Energy Secretary, last month called opponents of the plans “curmudgeons and fault-finders” and described turbines as “elegant” and “beautiful”.

The Duke’s attack on the turbines, believed to be the first public insight into his views on the matter, came in a conversation with the managing director of a leading wind farm company.

When Esbjorn Wilmar, of Infinergy, which builds and operates turbines, introduced himself to the Duke at a reception in London, he found himself on the end of an outspoken attack on his industry.

“He said they were absolutely useless, completely reliant on subsidies and an absolute disgrace,” said Mr Wilmar. “I was surprised by his very frank views.”

Mr Wilmar said his attempts to argue that onshore wind farms were one of the most cost-effective forms of renewable energy received a fierce response from the Duke.

“He said, ‘You don’t believe in fairy tales do you?’” said Mr Wilmar. “He said that they would never work as they need back-up capacity.”

One of the main arguments of the anti-wind farm lobby is that because turbines do not produce electricity without wind, there is still a need for other ways to generate power.

Their proponents argue that it is possible to build “pump storage” schemes, which would use excess energy from wind power to pump water into reservoirs to generate further electricity in times of high demand and low supply.

It emerged last year that electricity customers are paying an average of £90 a year to subsidise wind farms and other forms of renewable energy as part of a government scheme to meet carbon-reduction targets.

Mr Wilmar said one of the main reasons the Duke thought onshore wind farms to be “a very bad idea” was their reliance on such subsidies.

The generous financial incentives being offered to green energy developers have led landowners to look to build wind farms on their estates, including the Duke of Gloucester, the Queen’s cousin.

Prince Philip, however, said he would never consider allowing his land to be used for turbines, which can be up to 410ft tall, and he bemoaned their impact on the countryside.

Mr Wilmar said: “I suggested to him to put them on his estate, and he said, ‘You stay away from my estate young man’.

“He said he thought that they’re not nice at all for the landscape.”

The Duke’s comments echo complaints made by his son, the Prince of Wales, who has refused to have any built on Duchy of Cornwall land.

Yet a turbine will be erected opposite the Castle of Mey in Caithness, where he stays for a week every August, if a farmer succeeds in gaining planning permission from Highland Council.

While they are opposed to onshore wind farms, the Royal family stands to earn millions of pounds from those placed offshore.

Last year, the Crown Estate, the £7billion land and property portfolio, approved an increase in the number of sites around the coast of England. The Crown Estate owns almost all of the seabed off Britain’s 7,700-mile coastline.

Experts predict that the growth in offshore wind farms could be worth £250million a year. Britain has 436 offshore turbines, but within a decade that number will reach nearly 7,000. From 2013, the Royal family’s Civil List payments will be replaced, and instead they will receive 15 per cent of the Crown Estate’s profits, although the Queen, the Duke, the Prince of Wales and other members of the family do not have any say over how the estate makes its money.

Mr Wilmar was at a reception last week in Chelsea, west London, marking the 70th anniversary of the Council of Christians and Jews at which the Queen and Duke were guests of honour.

The Dutch businessman’s company describes itself as committed to preserving the planet. Infinergy, which is a subsidiary of the Dutch firm KDE Energy, is planning to build on a number of sites across the country, from the north of Scotland to Totnes in Devon.

Mr Wilmar claims that onshore turbines are less reliant on subsidies and more cost-effective than those built in the sea. “If you go offshore it costs you twice as much as being on-shore because you have to lay foundations in the sea,” he said. “It’s very expensive for very obvious reasons.”

Two-thirds of the country’s wind turbines are owned by foreign companies, which are estimated to reap £500million a year in subsidies.

A spokesman for the Duke said that Buckingham Palace would not comment about a private conversation.